The hepatic microsomal drug metabolizing enzyme is a monooxygenase consisting of several forms of cytochrome P-450 (cyt. P-450), NADPH-cyt. P-450 reductase and phospholipid. The complex has been resolved and the reductase and at least three forms of cyt. P-450 have been purified to homogeneity. The purified P-450's have been shown to differ in catalytic, spectral, physical and immunological properties, implying that they are under different gene control. The monooxygenase oxidizes a large number of diverse chemical compounds and is affected by several factors including age, sex and hormones. Almost invariably hormonal imbalance either induced by the administration of hormones or the removal of the endocrine organ results in impaired hepatic drug metabolic activity as measured with a number of substrates. The objective of this research proposal is to identify which cyt. P-450 in the hepatic microsomal fraction is regulated by adrogens. This proposal will examine the effect of testosterone in neonatal and postpubertal castrated rats on the oxidative activity of the microsomal fraction toward several substrates and the cyt. P-450 profile. The latter will be determined: 1. immunologically with antibodies toward each cyt. P-450; 2. by separating the hemeproteins by chromatography, identifying the hemeprotein by several criteria including regiospecific hydroxylation with selected substrates. Since the effect of castration on the hepatic microsomal monooxygenase in adult animals is reversible by testosterone administration, it provides an experimental approach for the isolation of mRNA specific for androgen sensitive cyt. P-450, which can be translated in vitro in an heterologous system and the product identifid by a number of means. This project intends to examine the reductase and phospholipid following the endocrine manipulation to determine whether these components contribute to the impaired monooxygenase activity. The data obtained in these studies would provide new information on the role of hormone on the monooxygenase which has proved to be a detoxificating and a carcinogen activating system.